Techniques for ion beam depositing DLC are known in the art. Typically, a layer of DLC which is ion beam deposited on a glass substrate is deposited using a constant voltage (or ion energy, which is related to but different than the anode-cathode voltage per se as will be explained below) thereby resulting in a layer of DLC having a constant density.
For example, consider a situation where a layer of DLC is ion beam deposited directly on a glass substrate using a voltage of about 3,000 V. The high voltage, between the anode and cathode of the ion source, causes ions to be accelerated toward the substrate to be coated with such high energy that significant ion mixing at the glass/DLC interface can occur. In particular, significant ion mixing between Si and C at the interface occurs thereby leading to many Si-C bonds. Unfortunately, such Si-C bonds in the DLC layer are believed to be more susceptible to breaking down upon exposure to ultraviolet (UV) radiation and water (i.e., QUV) than are C—C and C—H bonds. Thus, the presence of many Si-C bonds in a layer of DLC, especially a very thin layer of DLC such as from 20-100 Åthick, can lead to premature breakdown of the layer upon environmental exposure (i.e., reduced longevity).
Thus, it can be seen that DLC layers that are deposited using a constant voltage (especially a high voltage used to deposit a thin DLC layer) are problematic in that their lifetime is rather short due to the high amount of ion mixing at the glass/DLC interface. This high amount of ion mixing, and the large number of resulting Si-C bonds, renders the DLC layer more susceptible to breaking down upon environmental exposure.
In view of the above, it will be appreciated by those skilled in the art that there exists a need in the art for a technique for depositing a DLC inclusive layer(s) that is more durable and/or has improved longevity.